This invention relates to a two-stroke multi-cylinder engine and more particularly to an improved porting arrangement for an engine of this type.
Multi-cylinder two-cycle internal combustion engines frequently are constructed so the cylinder bores are disposed in nonaligned relationship. The cylinder bores are placed at an angle to each other (either V-type or opposed-type). It has been the practice to arrange the porting for the engine so that the exhaust ports for one bank lie on the opposite side of the cylinder bore of that bank from the exhaust ports of the other bank. The transfer passages are similarly arranged so that they lie on one side of one bank and the opposite side of the other bank. This is done frequently so as to permit the simplification of the port configuration and the manifolding associated with the exhaust ports.
For example, in V-type engines it is a normal practice to place both of the exhaust ports and the associated exhaust manifolding in the valley of the V. As as result, the transfer passages are grouped on the outside of the banks of the V. Although this provides simplicity of operation, it gives rise to a problem which can be best understood by reference to FIG. 1 which is a showing of the cylinder piston and connecting rod of one of the banks. In a typical configuration, this will be the positioning of the components of the right-hand cylinder bank.
In referring to FIG. 1, the right-hand cylinder bank of a V-type engine is identified by the reference numeral 11 and is formed with one or more cylinder bores 12 in each which a respective piston 13 reciprocates. The piston 13 is connected by means of a piston pin 14 to one end of a connecting rod 15. The opposite end of the connecting rod 15 is journaled upon a throw 16 of a crankshaft 17 for driving the crankshaft 17 upon reciprocation of the piston 13. The piston 13 further has one or more grooves in which piston rings 18 are supported for sealingly engaging the cylinder bore.
An exhaust port 19 opens through one side of the cylinder bore 14, normally the side facing the valley of the V of the engine. This exhaust port 19 is displaced to the left side of the center line of the bore 12 which center line is identified by the reference numeral 21. In a similar manner, one or more transfer passages which terminate in transfer ports 22 are disposed on the opposite (right) side of the cylinder wall 12 from the exhaust port 19.
The piston 13 is driven downwardly by the pressure of the expanding combustion gases under the force P. The angular relationship of the connecting rod 15 in driving the crankshaft 17 in the direction N causes a reactive force F to be directed through the connecting rod that causes a side force H to be exerted on the piston 13. This side force causes the piston 13 to cock slightly in the cylinder bore 12 (shown in exaggerated form in FIG. 1). Because of this cocking, the lower portion of the skirt of the piston 13 is forced into tight engagement with the portion of the cylinder wall 12 surrounding the exhaust port 19. This portion of the cylinder wall is considerably hotter than the intake port side due to the presence of the exhaust port 19 therein. Hence, with a conventional engine there is the danger of a seizure or scuffing of the piston on the cylinder wall.
It is, therefore, a principle object of this invention to provide a multi-cylinder engine in which this condition will not occur.
It is a further object of this invention to provide a multi-cylinder two-cycle crankcase compression internal combustion engine wherein the cylinder banks have their ports arranged in such a manner that the loading of the pistons and thermal conditions thereon are the same from one bank to another.